Explanation:
This wide, detailed
Spitzer Space Telescope view
features infrared light from dust (red) and old stars (blue)
in Andromeda, a massive spiral galaxy
a mere 2.5 million light-years away.
In fact, with over twice the diameter of
our own Milky Way,
Andromeda is
the largest nearby galaxy.
Andromeda's population of bright young stars define its sweeping
spiral arms in
visible light images, but here
the infrared view clearly follows the lumpy dust lanes heated by
the young stars as they wind even closer to the
galaxy's core.
Constructed to explore Andromeda's
infrared brightness and
stellar populations, the full mosaic image is composed of
about 3,000 individual frames.
Two smaller companion galaxies,
NGC 205 (below) and
M32 (above)
are also included in the combined fields.
The data confirm that Andromeda (aka M31) houses around 1
trillion
stars, compared
to
4 hundred
billion
for the Milky Way.